Wave source position detecting system



United States Patent Oil ice 3,134,977 Patented May 26, 1964 3,134,977 WAVE SOURCE POSITEON DETECTING SYSTEM Masateru Takagi and Masao Kumano, Tokyo, Japan, as-

signors to Nippon Electric Company Limited, Tokyo, Japan, a corporation of Japan Filed Oct. 6, 1%6, Ser. N 60,834 3 Claims. (Cl. 343-112) This invention relates to a system for detecting a source of radiant energy, and more specifically to such a systern which determines the position of the source by correlation techniques.

' Systems are known for determining the location of a source of radiant energy which utilize diversity reception principles. These systems require at least two diverse or separately located receiving stations where the radiated energy is received and processed for strength, the strength or amplitude of the signals being used to determine the location of the wave source. Such sys tems have been known generally as radio frequency direction finding systems.

Systems for determining the location of a wave source generally are required to make such a determination at receiving locations which may be separated by long distances from the wave source. Accordingly, it is important in these systems that the strength of the signal at least exceed the noise level. However, as is well known, the spectrum of radio frequencies is becoming more crowded, which results in a higher noise level when operating in such a spectrum. The known systems are not capable of operating eflicientiy, or in many instances at all, Where the noise level is approximately equal to, or greater than, the level of the wave source energy.

Accordingly, it is a primary object of this invention to provide a system which is capable of determining the position of a wave source by minimizing the ambient noise level.

It is a further object of the invention to provide a system which operates on correlation principles and which employs a plurality of wave source receivers having selectively controlled radiation patterns.

In' accordance with an aspect of the invention, there is provided a system for detecting the position of a wave source by means of cross correlation functions between outputs of a plural number of wave receiving points. The invention is characterized in that the receiving points have directivity patterns which are directed at the wave source. By separating the receiving points by substantial distances, the novel system is capable of locating the position of the wave source.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a block diagram of an embodiment of the invention;

FIG. 2 is a simplified representation of a broadside antenna array showing the distribution of the elements;

FIG. 3 is a s'impiified schematic diagram of a directivity synthesizing circuit; and

FIG. 4 is a radiation lobe pattern of the antenna array.

In FIG. 1, 11 and 12 suggest two positions spaced a distance and apart where plural numbers of receiving elements are arranged in order; 13 shows a signal source; a and B are angles taken by viewing 13 from 11 and 12 respectively; r and r are lineal distances measured from 11 and 12 to 13 respectively.

At each position 11 and 12, there is located a broadside array each consisting of 1-11 receiving elements in line, as shown in FIG. 2. The numerals 4 and 5 of FIG. 1 indicate multiple directivity synthesizing networks connected to the receiving elements at the positions 11 and 12 respectively and their outputs form directional groups of in channels whose main lobes are arranged in equal angular spacing within a search sweep or scope.

FIG. 3 shows an example of one such directivity synthesizing network for only one channel. Each complete directivity synthesizing network 4 and 5 consists of m sub-networks or sections, each having a construction as shown in FIG. 3. All corresponding input terminals 1', 2, 3. .n' of the m network sections are connected together for connection, in turn, to the corresponding signal receiving elements 1, 2, 3. .n. The output terminals a, b, of the network section shown in FIG. 3 are connected, respectively, by means of the wires 4a and 4b to the left side of the cross-correlator 6. Thus the network section of FIG. 3 has two outputs connected to the cross-correlater input, one between the terminal a and ground and the other between the terminal b and ground. The output terminals of the additional m network sections are connected to the left side of the cross-correlater 6 by means of additional wires represented by the dashed lines 40, 4d and 42. Similar connections as just described connect the synthesizing network 5 to the right side of the cross-correlator 6. Characteristics of each directivity synthesizing circuit can be determined in such manner as to produce n main lobes in equal angular spacing within the scope of the desired search angle.

When the angle of the main lobe of the ith output is given as 71' of the directivity synthesizing network relative to the line of the array, then the phase shift m which must be given between adjacent elements in the array should satisfy the following Equation 1 as is known from the theory of linear broadside arrays:

where k represents wave length and d represents distance between elements which are equallyv spaced.

In such a multiple directivity synthesizing network, the directivity pattern of the ith output among n pieces is represented by Ri provided that 7 represents an angle between the signal source and the array. The pattern of R1 (7) would be represented in polar coordinates as shown in FIG. 4. Position of its main lobe would be at y=7i as indicated in Equation 1.

Now, assuming that the ith output signal of the synthesized directivity among m sections of the multiple directivity synthesizing network is Si (2). Then, Si (t) would be represented as followsf Si(t)=KiRi( w 2 where, Ki represents an amplitude coefiicient; i is a phase delay of the directivity synthesizing network; 7 is a direction of signal source and r is the distance to the signal source.

If the ith output voltage of network 4 (associated With antenna sections at the position 11) hereinafter called the 1st set, is Si (t) and that the jth output voltage of network (associated with antenna sections'at the position 12) hereinafter called the 2nd set, is Sj (t), and if 'y and r are substituted by a, ,6 and r r respectively, then the following equations would be established.

If the noise is represented by m (1?) and M (1) is superposed on Si (t) and Sj (t) respectively, the ith and jth output of each set would be as follows:

would be-defined as follows:

'(1) 12)" LI (1) (2) (11hr h 2T ht (t)h] (t )dt nam fi omnm (10 The cross-correlator 6 in FIG. 1, is a conventional instrument which calculates a cross-correlation function between the i output of the 1st set and the 1' output of Zndset (i and j being in sections of 1, 2, 3 m) so that Aij(a,fl) could be obtained simultaneously. For information on such a cross-correlator, reference is here by made to A Computer for Correlation Functions by F. E. Brooks, Jr; et al., appearing in the Reviewof; Scientific Instruments, vol. 23, No. 3, pp. 121-1 26, 7 March 1952. a V 7 Now we shall examine the nature of'Aij(a,B)', Ri(a) would be maximum, when ot='yl' as indicated in Equation 1. As i is distributed in an equal angular spacing within a search scope and a is a continuous variable, a does not become exactly equal to i, but Ri(op)iwould be large when i is close to it, otherwise it would be small.

As all of ki could be made equal, Aij(a,}8) would be- 7 come oi=' i, ;3='yj or would be maximum when i, 1' are in the neighborhood of it. 7

Accordingly, if the maximum of thetAij(a,;3)s is known, i and j, "yi and 7] subsequently cc and B would also be known. W Thus, the position of the signal source can be determined. Moreover, the more accurate the cross-' correlator is, the more completely the influence of noise would be reduced.

Needless to say, there is no inconvenience in obtaining cross-correlation functions one after ianother by using a singledirectivity beam, when it is not necessary to obtain a result in a short time. f i V 1' For simplification of explanation, we have cited a broadside array ,wherein'the receiving elements, are ar- By this reason, the improvement in the degree of signal to noise ratio might be'lirnited for some extent.

When an approximate device is used as cross-correlator; the 2nd to.4th terms inclusive become zero. We a shall treat the terms, however, as zero in thefollowing' V deductions. e

Under this supposition,

X sin dt 'a substitution 7 each of said receiving means includingsignal ranged in a straight-line.' However, this is not essential and may be applicable to any directive beam as far as t can be rotated. For instance, the receiving elements may be in a circular array or a vertically crossed loop-antenna,

etc. g a i t Further, if a receiving elementiis' arranged in a focal' plane of a suitable wave convergent system, for instance, parabola or lens,.ete., it is well-known that the output of each receiving element would be'biasedby the direction 1 of the'beam. This system, however, could be used as: V of the multipledirectivityrsynthesizing net work. i

' [While the foregoing description sets forth the princiy V ples of the invention in connection with specific appara-:,

tus; it is to'be understood that this description is made e only byway of example and not as a; limitation 'of the' scope ofthe-invention as 'se't'forth in the ObjCClSihGl'COf and in the acco'mpanying claims 4 What is claimed'is: 1

1 A signal receiving system for determiningthe loca- V tion of ;a source 'ofelectrorna'gnetic wave energy com-L prising means 'jat signals from saidv energy source,

each of said rece'iving means having a main lobe-pat tern covering a predetermined :area shared 'withthe lobe patterns'of the other receiving means, 1 '7 "thesizing means for providing output signals having" a phase and amplitude dependent} on theposition 'of u said source with respectto saidilobe patterns,

and means responsive to the ou'tputsignals from each a plurality offspaced positionsfor receiving l of said synthesizingrmeans fordeyeloping output signal information indicative of the location of said energy source.

2. The system according to claim 1 wherein said receiving means includes an antenna array having a plurality of equally spaced signal receiving elements, and wherein said synthesizing means comprises a network having a plurality of input terminals, each of said terminals being connected to a separate element of said antenna array.

3. The system according to claim 2 wherein each of said antenna arrays is oriented to produce radially ex- 1Q 6 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Proceedings of the I.R.E., vol. 38, October 1950, pp. 1165-1171.

The Journal of the Acoustical Society of America, vol. 29, No. 12, December 1957, pp. 1342-1347. 

1. A SIGNAL RECEIVING SYSTEM FOR DETERMINING THE LOCATION OF A SOURCE OF ELECTROMAGNETIC WAVE ENERGY COMPRISING MEANS AT A PLURALITY OF SPACED POSITIONS FOR RECEIVING SIGNALS FROM SAID ENERGY SOURCE, EACH OF SAID RECEIVING MEANS HAVING A MAIN LOBE PATTERN COVERING A PREDETERMINED AREA SHARED WITH THE LOBE PATTERNS OF THE OTHER RECEIVING MEANS, 